Study On The Key Techniques Of Ultra-precision Polishing Of Aluminum Alloy Mirrors

Aluminum alloy is a common material for structural components and optical elements in aerospace optical systems.Aluminum alloy mirrors are widely used for the typical applications in the near infrared(NIR)and infrared(IR)wavelengths,and have a bright future in the visible(VIS)and ultra-violet(UV)range.The technique of single point diamond turning(SPDT)can fabricate directly the surfaces applied in the IR optical applications.But it is difficult to manufacture the mirrors which meet the higher requirements of optical performance.The difficulty in the ultra-precision processing of aluminum mirrors is that the aluminum alloy is soft and with low hardness.So it is easy to result in mechanical damage,surface defects such as scratches and wear during the forming processes,which decreases the surface smoothness and brightness.Further,the defects prone to corrosion,and the chemical stability of the surface becomes poor.These problems largely limit the manufacturing accuracy and applications for aluminum alloy mirrors.Therefore,it is necessary to develop the key techniques of ultra-precision polishing of aluminum alloy mirrors for the engineering demand of aluminum space cameras for the NIR,VIS and even UV wavelengths.The main contents of this paper are divided into the following points:1.Exploring the typical aluminum mirror surface micro morphology,elemental composition and physical properties by scanning electron microscope(SEM),energy dispersive spectrometer(EDS),and Nano-identation,and establishing the relationship between the 3 characteristics of surface.Analyzing the causes of surface defects from the characteristics of aluminum alloy and SPDT mechanism.Research of the evolution of aluminum mirror surface roughness,microstructure and elements during the different polishing processes is developed.And improving the surface quality of aluminum mirror according to the efficiency balance theory of chemical mechanical polishing(CMP).2.The influence of the surface quality of aluminum alloy mirror on it's reflectivity is investigated.And the improvement of the reflectivity and effect of optical coating on the surface of aluminum alloy mirror is verified by the contrast experiments.3.Aiming at the demand of the shape correction of aluminum mirror,the combined figuring process is proposed.The cleaning and storage methods of aluminum alloy mirrors are studied,and improving the combined figuring process in details.Analyzing the factors which result in the errors of aluminum mirror surface profile measurement.At last,carrying out the experimental verification of ultra-precision polishing of plane and aspherical aluminum mirrors.